UNIVERSITY  OF  CALIFORNIA  agricultural  Experiment  Station 

COLLEGE  OF  AGRICULTURE  E.  J.  WICKSON,  DIRECTOR 

BERKELEY,  CALIFORNIA 


CIRCULAR  No.  76 

(August,  1911) 


HOT  ROOM  CALLUSING 


FREDERIC  T.  BIOLETTI  and  LEON  BONNET 


Nursery  of  Bench  Grafts. 


SACRAMENTO 
Friend  Wm.  Richardson     -     -     -     Superintendent  of  State  Printing 

1912 


r 


CONTENTS. 


Page. 

1.  Defects  of  Ordinary  Methods 3 

2.  Methods  of  Grafting 4 

3.  Graft   Trays 5 

4.  Callusing  Boxes 5 

5.  Callusing  Materials 6 

6.  Filling  the  Boxes 8 

7.  Hot  Room • 8 

8.  Temperature    0 

9o     Moisture 9 

10.  Aeration  10 

11.  Removal  from  Hot  Room 11 

12.  Hardening    11 

13.  Planting 12 


HOT  ROOM  CALLUSING. 

1.  Defects  of  Ordinary  Methods*  In  the  production  of  grafted 
resistant  vines,  it  is  necessary,  after  the  cuttings  are  grafted,  to  callus 
them  before  planting  in  the  nursery.  This  callusing  consists  in  the 
formation,  on  the  cut  surfaces  of  stock  and  scion,  of  healing  tissue  by 
which  the  union  is  brought  about.  For  this  process  certain  conditions 
of  moisture  and  temperature  are  required.  These  conditions  are 
obtained  by  stratifying  the  grafts  in  "callusing  beds"  of  sand  as 
described  in  Bulletin  180. 


Fig.   1. — Grafting  house,   south  front,   showing  sand  callusing  beds. 

The  sand  callusing  bed  has  many  defects  and  inconveniences.  It  has 
too  much  dependence  on  weather  conditions.  If  the  weather  is  cold 
the  cuttings  remain  dormant  so  long  that  they  may  rot  or  dry  out  before 
callus  forms.  If  the  weather  is  warm  they  may  callus  too  soon,  and, 
before  the  nursery  is  in  condition  for  planting,  the  buds  and  roots  may 
have  grown  so  much  that  many  are  killed  or  injured  in  removing  to 
the  ground.  Even  with  the  most  favorable  weather,  the  callusing  is 
completed  at  various  times  owing  to  the  grafting  being  carried  on  for 
several  weeks  or  months,  and  it  requires  constant  care  and  vigilance 

*For  a  discussion  of  the  general  practice  of  resistant  vine  grafting  and  callusing 
the  reader  is  referred  to  Bulletin  180,   "Resistant  Vineyards." 


to  catch  the  grafts  at  exactly  the  best  stage  for  planting.  It  is  difficult 
or  impossible  to  construct  a  sand  bed  in  which  the  condition  of  tem- 
perature and  moisture  are  uniform  in  all  parts.  In  one  part  of  the  bed 
some  of  the  grafts  will  have  progressed  too  far,  while,  in  another,  grafts 
of  the  same  kind  made  at  the  same  time  will  have  hardly  started  to 
callus. 

The  period  of  callusing  will  vary,  under  identical  conditions,  with 
the  variety  of  stock  and  scion.  Where  several  varieties  are  being 
grafted  some  must  be  planted  too  soon  and  some  too  late,  unless  separate 
beds  are  used  for  each  combination,  which  is  troublesome  and  imprac- 
ticable. All  these  irregularities  not  only  diminish  the  percentage  of 
first  class  vines  produced,  but  the  special  care  needed  greatly  increases 
the  labor  and  cost.  The  handling  of  grafts  in  a  sand  bed  makes  it 
necessary  that  stock  and  scion  should  be  very  firmly  held  together. 
-This  necessitates  tying  the  grafts  at  a  costVlmost  equal  to  the  actual 
grafting,  and  also  the  removal  of  the  tying  material  in  the  nursery 
•which  is  both  troublesome  and  expensive. 

The  method  of  stratifying  in  boxes  of  moss  and  callusing  in  a  hot 
room  overcomes  many  of  these  difficulties,  and  has  therefore  been 
adopted  by  all  the  large  producers  of  grafted  vines. 

2.  Methods  of  Grafting.  When  stratified  in  moss,  the  grafts  are  not 
subjected  to  any  rough  handling  and  it  is  therefore  unnecessary  to  tie 
them.  The  ordinary  "whip"  graft,  however,  is  unsuited  to  this  pur- 
pose because  the  cut  surfaces  will  not  remain  in  contact  unless  they  are 
tied.  Two  forms  have  been  found  suitable,  *.  e.,  the  "Wire  graft/'  and 
a  "Modified  whip  graft."  The  former  is  fully  described  in  Bulletin 
180.  It  is  peculiarly  suited  to  beginners,  owing  to  the  ease  with  which 
it  can  be  made  without  practice.  It  would  undoubtedly  be  more  used 
by  nurserymen  but  for  an  unfounded  prejudice  that  the  wire  is 
injurious  to  the  vine.  To  make  this  graft,  stock  and  scion  of  the  same 
diameter  are  cut  at  an  angle  of  about  45°  and  kept  in  contact  by  means 
of  a  piece  of  No.  17  gauge  galvanized  iron  wire,  about  2  inches  long, 
inserted  in  the  pith.  Stock  and  scion  should  be  pressed  together  firmly 
and  it  is  usually  best  to  use  two  pieces  of  wire. 

The  modified  whip  graft  differs  from  the  ordinary  form  principally 
in  the  angle  of  the  bevel  and  the  position  of  the  tongue.  The  bevel  is 
made  nearly  as  steep  as  for  the  wire  graft.  The  length  of  the  cut  is 
about  1.75  times  the  diameter  of  the  cutting,  which  corresponds  to  an 
angle  of  about  35°.  In  the  ordinary  whip  graft,  the  cut  is  made  from 
2.5  to  3.5  times  the  diameter  of  the  cutting.  The  shorter  bevel  does 
away  with  the  tendency  of  the  points  to  draw  apart.  The  tongue  com- 
mences much  nearer  the  top  of  the  cut  in  this  form  and  reaches  nearly 
to  the  bottom.    It  is  made  by  a  sliding  motion  of  the  knife  from  left  to 


—   0 


right  or  in  the  reverse  direction.  In  withdrawing  the  knife  the  point 
of  the  tongue  is  bent  out  by  a  twist  of  the  knife  in  order  to  facilitate 
the  putting  together  of  stock  and  scion.  The  tongue  is  made  by  cutting 
slightly  across  the  grain,  as  in  ordinary  whip  graft,  but  is  slightly 
thicker  than  in  the  latter  case. 

When  properly  made,  grafts  of  this  kind  hold  together  very  firmly 
and  resist  lateral  and  longitudinal  displacement  sufficiently  for  hand- 
ling. Figure  2  shows  the  two  methods  described  in  comparison  with 
the  ordinary  whip  graft. 

3.  Graft  Trays.  While  properly  made  grafts  hold  together  with 
considerable  firmness,  the  less  and  the  more  carefully  they  are  handled 


1 


A  B  C 

Fig.  2. — A,  Wire  graft ;  B,  Modified  whip  graft ;  C,  Ordinary  whip  graft. 

the  fewer  will  fail.  With  this  object,  graft  trays  or  stands  are  useful. 
Each  grafter  is  usually  furnished  with  a  shallow  tray  in  which  he 
places  the  grafts  as  he  makes  them  and  in  which  they  are  carried  to 
the  callusing  boxes.  Stands  like  that  illustrated  in  Fig.  3  are  better. 
This  stand  consists  of  a  piece  of  ^-inch  board  16  inches  by  9J  inches, 
furnished  with  a  3^-inch  cleat  at  the  back  to  hold  the  grafts,  a  H-inch 
cleat  at  the  front  to  protect  the  unions,  and  two  legs  to  keep  the  stand 
at  a  convenient  angle.  Such  a  stand  will  hold  from  fifty  to  one  hundred 
grafts  and  protect  them  from  injury  when  carried  and  handled  with  a 
minimum  of  labor  and  care. 

4.     Callusing  Boxes.     The  sizes  of  the  boxes  may  vary,  but  for  ease 
of  handling  there  is  a  practical  maximum.    When  grafting  is  practiced 


—  6  — 

on  a  large  scale,  boxes  40  inches  in  length  and  20  inches  in  width  are 
generally  used.  The  depth  varies  according  to  the  length  of  the  grafts. 
It  should  be  at  least  from  8  to  10  inches  longer  than  the  grafts,  or  for 
Californian  conditions  about  22  to  24  inches  in  all.  On  a  small  scale  it 
is  better  to  have  smaller  boxes.  Their  handling  and  the  separation  of 
the  varieties  are  very  much  facilitated.  For  two  years  boxes  like  those 
represented  in  Fig.  4  have  been  used  successfully  at  the  University 
Farm,  at  Davis.  Such  boxes  measure  25  inches  in  depth,  16  inches  in 
width,  19^  inches  in  length,  and  will  hold  from  450  to  500  grafts,  accord- 
ing to  the  thickness  of  the  cuttings.  In  order  to  facilitate  the  placing 
of  the  grafts  in  the  boxes  and  their  removal,  one  of  the  shorter  sides 


Fig.  3. — Graft  stand. 

should  be  attached  by  means  of  screws,  or  by  a  slit,  so  as  to  be  easily 
removable.  The  bottoms  of  the  boxes  must  be  perforated  with  several 
rows  of  small  holes,  which  allow  the  excess  of  water  to  drain  off  after 
dipping  as  described  later.    The  tops  of  the  boxes  remain  open. 

5.     Callusing  Materials.     The   material  used   for   filling   the   boxes 
must  present  the  following  characteristics: 

1.  High  retentive  power  for  water. 

2.  Ease  of  aeration. 

3.  Freedom  from  molds. 

4.  Lightness. 

5.  Cheapness. 

The  first  three  conditions  are  necessary  for  the  proper  formation  and 


_  7  — 

development  of  healing  tissue.     The  fourth  facilitates  the  handling  of 
the  boxes. 

Among  the  numerous  callusing  materials  tried  with  this  method  a 
few  fully  answer  the  above  requirements.  They  are:  seaweed,  moss 
and  sawdust,  with  each  of  which  charcoal  is  added  for  its  antiseptic 
properties.  Experience  has  shown  that  a  mixture  of  two  thirds  moss 
and  one  third  charcoal,  and  one  of  two  thirds  sawdust  and  one  third 


Fig.  4. — Callusing  box  and  dipping  vat. 

charcoal  give  satisfactory  results.  The  first  of  these  mixtures  is  used 
as  a  bottom  and  lateral  covering,  the  other  as  a  filling  and  a  top  cover- 
ing. The  charcoal  must  be  sifted  and  the  biggest  particles  must  not  be 
larger  than  peas.  These  materials  are  mixed  beforehand  to  be  ready 
when  needed.  The  moss  is  first  soaked,  drained  and  spread  on  a  clean 
floor,  charcoal  is  then  added.  Two  or  three  alternating  layers  of  moss 
and  charcoal  are  put  together  and  the  mass  is  uniformly  mixed.  If  the 
mixture  appears  too  dry,  water  is  added  by  sprinkling.     For  the  saw- 


dust-charcoal  mixture  it  is  better  to  mix  the  dry  components  and  add 
water  afterwards. 

6.  Filling  the  Boxes.  With  the  above  described  mxtures  at  hand, 
a  callusing  box  is  placed  with  the  short  side  down  and  the  removable 
side  open  and  on  top.  The  other  sides  of  the  box  and  part  of  the  bottom 
receive  a  uniform  hand-pressed  layer  of  moss  and  charcoal  two  inches 
thick  and  the  grafts  are  laid  horizontally,  stocks  toward  the  bottom  and 
scions  exactly  at  the  same  distance  from  the  normal  top  of  the  box. 
After  two  or  three  layers  of  grafts  have  been  placed  in  this  way,  a  thin 
layer  of  the  sawdust-charcoal  mixture  is  sprinkled  over  them.  The 
coating  of  moss-charcoal  is  now  carried  up  the  long  sides  and  bottom 
a  few  inches  higher  and  another  layer  of  grafts  added.  When,  in  this 
manner,  the  box  is  filled  up  to  within  two  inches,  the  remaining  space 
is  filled  with  the  moss-charcoal  mixture.  The  removable  side  is  then 
fixed  in  place  and  the  box  set  upright.  The  scions  are  just  covered 
with  the  sawdust-charcoal  mixture  and  the  box  dipped  in  water.  After 
a  few  moments  immersion  it  is  put  aside  to  drain. 

For  this  purpose  a  dipping  tank  or  vat  is  needed.  This  should  be  a 
little  larger  than  the  callusing  boxes  used,  conveniently  placed  and  with 
some  means  of  filling  it  with  warm  water.  The  dipping  vat  used  at 
Davis  is  shown  in  Fig.  4.  It  is  made  of  concrete  and  supplied  with  a 
steam  pipe  by  means  of  which  the  water  can  be  raised  to  the  desired 
temperature.  It  is  filled  by  means  of  a  hose  and  emptied  by  a  tap  at 
the  bottom  communicating  with  a  drain. 

After  the  excess  of  water  has  drained  out  of  the  box,  if  the  mixture 
has  sunk,  its  original  level  is  reestablished  by  adding  more  of  the  saw- 
dust-charcoal. A  layer  2  inches  thick  of  excelsior,  softened  by  soaking 
in  water,  is  then  put  directly  on  top  of  the  scions.  On  this,  a  piece  of 
sacking,  exactly  fitting  the  top  of  the  box  is  placed  and  in  turn  received 
a  two  to  three  inch  layer  of  the  sawdust-charcoal  mixture.  The  excelsior 
allows  the  development  of  the  buds  and  proper  aeration.  The  piece  of 
sacking  facilitates  watching  the  progress  of  callusing  and  any  necessary 
changes  of  the  covering. 

7.  Hot  Boom.  The  hot  room  must  be  of  convenient  size  and  shape 
to  facilitate  handling  the  boxes.  The  boxes  may  be  placed  in  two  or 
three  superposed  layers  on  shelves  or  trestles.  A  space  of  several  inches 
should  be  left  between  them  and  the  wall  and  between  the  sides  of 
adjacent  boxes. 

Windows  or  other  apertures  should  be  so  spaced  as  to  insure  even 
and  complete  ventilation.  Light  is  unnecessary  and  the  direct  rays  of 
the  sun  should  be  avoided. 

Any  heating  system  which  will  maintain  an  even  temperature  may 
be  used.    A  small  coal  oil  stove  is  sufficient  for  a  small  room.    Hot  water 


or  steam  heating  appliances  are  preferable  for  large  scale  operations. 
With  well  insulated  walls  in  ordinary  weather  the  heat  can  be  kept 
sufficiently  constant  without  a  fire  at  night. 

If  there  is  any  considerable  difference  of  temperature  in  various 
positions,  as  when  the  boxes  are  in  superposed  layers,  it  is  necessary  to 
change  the  position  of  the  boxes  occasionally  in  order  to  insure  even 
callusing. 

8.  Temperature.  Heat  is  a  necessary  factor  in  the  formation  of 
healing  tissue.  The  temperature  of  the  hot  room,  as  said  before,  must 
be  kept  regular.  The  heating  of  the  room  should  be  started  before  the 
boxes  are  placed  there  until  the  desired  temperature  becomes  uniform. 
A  well  equipped  callusing  room  should  possess  a  maximum  and  min- 
imum thermometer,  mounted  on  a  piece  of  board  fixed  to  the  wall  at 
five  feet  from  the  ground  and  on  the  opposite  wall  an  ordinary  ther- 
mometer. At  what  temperature  the  room  should  be  kept  depends  on 
the  result  desired.  To  determine  this  it  is  necessary  to  know  the 
characteristics  of  a  well-callused  graft.  Such  a  graft  shows  healing 
tissue  formed  all  around  the  cut  surfaces  and  in  sufficient  quantity  to 
cause  them  to  unite.  It  should,  after  a  certain  time,  be  strong  enough 
to  withstand  a  pull  of  several  pounds  without  breaking.  The  scion 
buds  should  be  dormant  or  only  slightly  sprouted.  This  can  be  obtained 
by  keeping  the  temperature  of  the  room  between  70°  and  80°  F.  At 
these  temperatures  it  will  require  between  twenty  and  fifteen  days  to 
produce  a  good  union  of  stock  and  scion.  At  86°  F.,  the  formation  of 
callus  is  much  quicker  and  can  be  obtained  in  about  ten  days,  but  the 
callus  is  of  a  softer  texture  and  has  a  tendency  to  grow  too  large.  With 
certain  precautions,  this  temperature  can  be  used  when  grafting  is  done 
very  late  in  the  season. 

When  grafting  is  started  early  in  the  season,  the  callusing  is  done  at 
about  77°  and  in  two  different  ways.  In  one,  the  grafts  are  callused 
immediately  and  then  kept  in  a  cool  place  until  planted,  in  the  other, 
the  grafts  are  kept  in  a  cool  room  at  a  tempeerature  of  about  60°  F., 
and  callusing  in  the  hot  room  commenced  about  2  weeks  before  the  time 
for  planting.    The  former  method  is  most  convenient. 

9.  Moisture.  Another  important  factor  in  the  formation  of  healing 
tissue  is  moisture.  The  best  conditions  in  this  respect  occur  when  there 
is  sufficient  moisture  present  to  prevent  all  drying  of  the  cuttings 
without  forcing  root  formation.;/ In  a  sand  bed,  the  optimum  amount 
of  water  will  vary  from  2\  to  1\  per  cent  of  the  weight  of  the  sand. 
The  purer  and  coarser  the  sand,  the  less  water  needed.  The  finer  the 
sand  and  the  more  earthy  or  clayey  material  it  contains,  the  larger 
the  amount  of  water  it  will  hold  which  is  unavailable  for  the  grafts. 

The  degree  of  humidity  is  much  more  easily  controlled  in  callusing 


—  10  — 

boxes  than  in  sand  beds.  When  examination  shows  that  there  is  too 
much  moisture  at  the  level  of  the  unions  the  cover  of  sawdust,  sacking 
and  excelsior  is  removed  and  after  aeration  replaced  with  drier 
material.  Excess  of  moisture  is  evidenced  by  slowness  or  absence  of 
callus  formation  and  by  growth  of  mold.  The  cover  is  prevented  from 
becoming  too  dry  by  occasional  sprinklings  with  water  of  the  tempera- 
ture of  the  room. 

With  a  little  practice  it  is  easy  to  determine  the  most  favorable  degree 
oi"  humidity.  The  principal  danger  is  the  presence  of  too  much  water. 
Providing  the  excelsior  covering  feels  moist  to  the  hand,  there  is  no 
danger  of  the  unions  suffering  from  dryness. 

After  about  ten  days  in  the  hot  room  at  a  temperature  of  77°  F.,  the 


Fig.  5. — Cutting  shed  used  for  hardening  callused  grafts. 

boxes  are  dipped  in  warm  water  (77°-80°  F.).  The  boxes  should  be 
carefully  lowered  into  the  dipping  vat  so  that  the  water  gradually  enters 
the  holes  in  the  bottom  and  fills  the  box  nearly  to  the  level  of  the  unions, 
which  it  should  not  reach.  The  boxes  are  then  removed,  allowed  to 
drain  and  replaced  in  the  hot  room.  The  dipping  equalizes  the 
moisture,  stimulates  the  vital  processes  and  thoroughly  aerates  by 
renewing  the  air.  One  dipping  during  the  time  the  boxes  stay  in  the 
hot  room  is  usually  sufficient. 

10.  Aeration.  The  presence  of  oxygen  is  absolutely  necessary  for 
the  formation  of  healing  tissue.  Grafts  tied  with  raffia  in  such  a  way 
that  the  air  is  excluded  from  the  cut  surfaces  do  not  callus  well;  when 
tin  foil  is  used  in  a  similar  way  they  do  not  callus  at  all.    When,  by  an 


—  11  — 

excess  of  moisture  and  a  high  temperature,  a  fungus  film  forms  over 
the  unions,  the  air  is  excluded  and  callus  fails  to  form. 

The  hot  room  should  be  well  ventilated  and  the  box  covers  should  be 
arranged  to  give  all  the  aeration  needed. 

11.  Removal  from  Hot  Room.  When  the  desired  amount  of  callus 
has  been  formed  and  the  unions  are  complete  all  around,  the  boxes  are 
removed  from  the  hot  room.  At  this  stage  the  best  grafts  should  show 
indications  of  root  formations  and  a  slight  swelling  of  the  buds.  Others 
may  have  formed  shoots  of  half  an  inch  or  so  and  rootlets  of  the  same 
length.  This  condition  is  reached  with  most  varieties  in  about  fourteen 
days  at  a  temperature  of  77°  F. 

On  removal,  the  boxes  are  dipped  again  in  water  of  about  75°  F.  or 


Fig.    6. — Grafting  house,   north   front. 

just  a  little  below  the  temperature  at  which  they  have  been  kept.  Cold 
water  would  be  injurious  to  the  delicate  growing  tissues.  After  drain- 
ing, the  boxes  are  removed  to  a  cool  place  for  hardening. 

12.  Hardening.  Though  the  unions  are  nearly  complete  when 
removed  from  the  hot  room  the  grafts  cannot  safely  be  planted  imme- 
diately. The  callus  is  too  soft  and  delicate  to  be  exposed  to  the  cold 
and  varying  temperature  of  the  soil  without  suffering.  The  change 
must  be  gradual  to  give  time  for  the  hardening  of  the  new  tissues.  The 
boxes  are  therefore  stored  in  a  room  where  the  temperature  is  regular 
and  a  few  degrees  (10°  or  15°)  cooler  than  that  of  the  hot  room.  Here 
the  grafts  unite  more  thoroughly  and  gradually  become  accustomed  to 
a  lower  temperature.    After  a  week  in  this  room,  they  should  be  placed 


-  12  — 

outside  in  a  shed,  where  they  will  gradually  reach  the  mean  outside 
temperature.  In  this  shed  they  should  be  protected  from  the  direct 
rays  of  the  sun,  from  rain  and  from  drying  winds.  The  shed  shown  in 
Fig.  5  has  been  found  suitable  at  the  University  Farm.  They  may  be 
left  in  this  shed  for  several  weeks  if  necessary,  but  must  be  carefully 
watched  to  prevent  drying  out. 

Before  the  boxes  are  taken  to  the  nursery,  they  should  be  given  a  third 
dipping,  this  time  in  ordinal  cold  water.  This  will  protect  them  from 
drying  while  being  planted. 

13.  Planting.  The  callused  grafts  should  be  planted  as  soon  as  the 
nursery  soil  is  in  good  condition  and  the  temperature  of  soil  and  air 
are  favorable  to  growth.  The  best  time  is  at  or  a  little  before  the  start 
of  vegetation  in  the  vineyard.  A  great  advantage  of  this  method  is  that 
callusing  is  started  immediately  after  making  the  grafts,  while  the  cuts 
are  still  fresh  and  before  the  tissues  have  suffered  from  drying  or  too 
much  moisture.  An  equal  advantage  is  that  all  the  grafts  at  whatever 
time  they  are  callused  may  be  planted  at  the  same  time.  After  callusing 
they  are  simply  kept  dormant  in  the  cool  shed  until  weather  and  soil 
conditions  are  favorable  for  planting. 

When  everything  is  ready  the  boxes  are  removed  to  the  nursery, 
the  removable  side  taken  off  and  the  grafts  carefully  transferred  to 
shallow  boxes  or  trays.  If  any  of  the  grafts  have  formed  long  shoots 
or  roots,  these  should  be  trimmed  off  as  they  cannot  be  saved  and  it  is 
better  to  remove  them  before  planting.  If  the  weather  is  hot  or  dry  the 
trays  of  grafts  should  be  covered  with  a  wet  sack  until  they  are  planted. 

The  nursery  work  is  identical  with  that  used  in  the  ordinary  methods 
described  in  Bulletin  180  with  the  exception  that  there  is  no  tying 
material  to  remove. 


